This invention relates generally to pressure switches and more specifically to vented pressure switches adapted for use with hydraulic fluid control lines of a motor vehicle automatic transmission system.
In recent years, it has become conventional in the motor vehicle art to control various engine and powertrain functions by means of microprocessor based controls to obtain optimum performance. For example, actuation of valves used to effect transmission gear shifting are sensed by placing normally open and normally closed pressure responsive electrical switches in communication with hydraulic lines so that a change in pressure in such lines which occurs upon valve actuation and de-actuation can be sensed and a suitable electrical signal provided to the microprocessor as a result of the switching. Switch assemblies of this type are shown for example in U.S. Pat. Nos. 4,861,953; 4,853,503; 5,004,876; 5,015,808 and 5,101,549, all assigned to the assignee of the present invention.
The above referenced switches employ a pressure responsive member placed in pressure communication with hydraulic fluid in a control valve line. Upon a selected change in pressure of the fluid the pressure responsive member experiences a change from one configuration to another configuration and in so doing either closes or opens an electrical circuit which is adapted to provide a signal to the microprocessor of the particular change in pressure signifying the switching of a valve and a corresponding change in a transmission function. In order for the switching to be an accurate reflection of the change in pressure it is important that the switches have a consistent response time even with changing temperatures, actuation/release pressures, endurance life and so on. This in turn a hermetic enclosure for the switch contact system or a means for venting the switch contact system if the contact system operates immersed in oil (automatic transmission fluid) or a vented switch. Hermetic enclosures, however are prohibitive from a cost standpoint and therefore it is important to provide some means for venting the switching chamber. Another problem which must be dealt with is the environment of the switches. That is, the switches are mounted either totally immersed in fluid or in areas where they are splashed with fluids on a regular basis. These fluids contain contaminants such as chips or slivers from the transmission gears which are carried by the hydraulic fluid. These contaminants can have an adverse affect on switch operation. Normally open switches are particularly sensitive to contamination with large particles or slivers sometimes bridging the gap between the movable contact member when in the normal open position and the stationary contact thereby giving a false actuation signal to the microprocessor.
It is an object of invention to provide an inexpensive yet reliable pressure responsive electrical switch having improved insensitivity to contamination present in fluid in the switch environs. Another object of the invention is the provision of an improved vented pressure responsive electrical switch.